Future-generation communication systems are under development to provide high-speed, large-data transmission and reception services to mobile stations (MSs). For the high-speed data transmission and reception, future-generation communication systems adopt a multi-hop relay scheme. Multi-hop relay is a scheme of transmitting data via fixed or mobile RSs over multiple hops. When the channel status between a base station (BS) and an MS is poor, a multi-hop relay path is established and data is transmitted and received between the BS and the MS via RSs, thus providing a better radio channel to the MS. Therefore, with the use of the multi-hop relay scheme in a shadowing area experiencing severe shielding due to buildings, a communication service can be provided efficiently to a user (i.e., an MS). Also, the multi-hop relay scheme provides a better data channel to a cell boundary where an MS is in poor channel status and expands cell coverage.
An RS demodulates and decodes data received from a transmitter (i.e., a BS) and then encodes and modulates the demodulated and decoded data, prior to transmission to a receiver (i.e., an MS). This RS enables high-speed data transmission and reception by reducing path loss between radio links, and enables data transmission and reception even when the MS is remote from the BS or the MS is located in a shadowing area.
However, if a transmit antenna and a receive antenna are not substantially isolated from each other in the RS, a relatively strong signal (for example, a transmission signal) interferes with a relatively weak signal (for example, a received signal). Thus, different radio resources should be used for the transmission signal and the received signal. In the case where N RSs are taken to transmit one-frame data, the BS should use (N+1) times more resources than for direct transmission to an MS. As a result, the whole system capacity may be decreased. Now a description will be made of a comparison between the direct transmission and the relayed transmission in terms of radio resources (for example, slots) when the BS transmits one-frame data to the MS with reference to FIGS. 1A and 1B.
FIG. 1A illustrates slots taken to transmit a signal from a BS to an MS in a conventional communication system.
Referring to FIG. 1A, the BS transmits one-frame data directly to the MS in a single slot.
FIG. 1B illustrates slots taken to transmit a signal from a BS to an MS in a multi-hop relay communication system. Before describing FIG. 1B, it is assumed that the multi-hop relay communication system includes N RSs.
Referring to FIG. 1B, the BS transmits one-frame data to the MS via the RSs in a new slot on each of links BS-RS1, RS1-RS2, . . . , RSN-MS. Consequently, the BS requires (N+1) slots to transmit the one-frame data to the MS via the N RSs.
As described above, RSs enable high-speed data transmission and reception and also enable data transmission and reception even when an MS is remote from a BS or in a shadowing area in a multi-hop relay communication system. However, unless a transmit antenna is sufficiently isolated from a receive antenna in an RS, a relatively strong signal interferes with a relatively weak signal. The resulting requirement for using different time and frequency resources for each signal transmission leads to resource consumption. Also, the use of RSs wastes limited radio resources and thus decreases system capacity.